Objective—To determine the effects of treatment
with and without adjuvant radiation therapy on recurrence
of ocular and adnexal squamous cell carcinoma
(SCC) at specific anatomic locations in horses.
Procedures—Medical records of horses with histologically
confirmed ocular and adnexal SCC evaluated
from 1985 to 2002 were reviewed. Sex, breed, age,
type of treatment, location, and recurrence of SCC
were recorded. Two treatment groups determined by
recurrence of SCCs treated with and without adjuvant
radiation therapy were established.
Results—The anatomic site with the highest recurrence
rate was the limbus (junction of the cornea and
sclera) or bulbar conjunctiva (47.7%), independent of
treatment group. There was a significant difference in
recurrence rates of ocular and adnexal SCCs between
the 2 treatment groups, independent of anatomic location.
Recurrence rates of SCCs treated with and without
adjuvant radiation therapy were 11.9% and 44.1%,
respectively. Recurrence rates for SCCs of the eyelid,
limbus or bulbar conjunctiva, and cornea treated with
adjuvant radiation therapy were significantly different
from those for SCCs treated without adjuvant radiation
therapy. The most frequently represented anatomic
site for ocular and adnexal SCCs was the eyelid
(28.7%). Coat color, breed, and the interaction of age
and breed had a significant effect on tumor recurrence
regardless of treatment type and anatomic location.
Conclusions and Clinical Relevance—Results indicated
that ocular and adnexal SCCs treated with adjuvant
radiation therapy had a significantly lower recurrence
rate, compared with SCCs treated without adjuvant
radiation therapy, independent of anatomic location.
(J Am Vet Med Assoc 2004;225:1733–1738)